The present invention relates to closures for reclosable thermoplastic containers, and more particularly to such closures of the "wide track" variety, wherein ribs are formed generally adjacent and on either side of a male or female closure element.
Reclosable thermoplastic containers bearing such male and female closure elements are presently edge-sealed by several methods. A number of well-known and commercially-employed methods of forming these containers can be described as generally involving clamping film portions together, and moving a heated element against the clamped film portions. Such a method is described, for example, in commonly-assigned U.S. Pat. No. 4,396,449 to Tumminia (the '449 patent).
In a majority of the containers made by these several methods, leaks are formed at the ends of the closures, where film portions carrying the closure elements have been edge-welded or sealed together. These leaks can impair the usefulness and appeal of these containers to consumers, as is well-known, and the frequency and magnitude of leaks are matters of considerable concern for manufacturers of such containers.
Applicants have observed that the clamping of film portions in sufficiently close relationship to form a good edge-weld or seal therebetween can compress the male and female elements together to the point where the elements are distorted.
The closure elements are very often so severely distorted as to not permit a good fit between the elements. When the film portions carrying the male and female elements are sealed together, the poor fit is made permanent adjacent the edges or sides formed by the seal and leaks ensue through the ends of the distorted closure.
A groove has been previously employed in the clamping members of apparatus for carrying out a method as described in the '449 patent, for receiving the male or female closure element therein while the film portions which are to comprise the container are clamped together and for thus relieving some of the compressive stresses on the elements.
Despite the provision of such grooves, however, the male and female closure elements of reclosable thermoplastic containers made by this and like methods frequently still are compressed together and distorted to such an extent that leaks occur at the ends of the closures.